1. Field of the Invention
The present invention relates to a method and apparatus for preventing leakage of unfiltered fluid through a filter system. Particularly, the present invention is directed to a filter cartridge configured to prevent leakage of unfiltered fluid, as well as a filter system and method using the same.
2. Description of Related Art
Fluid and hydraulic systems are commonly used to satisfy a variety of commercial and domestic needs. A common problem shared by such systems, especially closed systems that continuously recycle fluid for reuse, is contamination. Soluble and insoluble contaminants become entrained in the fluid, often building up in system components and adversely impacting overall efficiency. Such contamination results in increased operating and maintenance costs, as well as possible disruption of service when acceptable contamination levels are exceeded. In fact, contamination actually may render some fluid or hydraulic systems useless if untreated, or if the system is sensitive to the presence of contaminants.
To address the problems associated with contamination, a variety of filtration and contaminant removal methods have been developed. One such method uses integral filter units, commonly known as filter cartridges, for the removal of contaminants. A conventional filter cartridge includes filter material held securely between opposite planar end walls. The filter material is configured into a tubular shape having a hollow center extending between the opposite planar end walls, and each planar end wall is provided with a central aperture in alignment with the hollow center. Outer and inner walls likewise extending between and securely connected to the planar end walls also may be provided to encase the filter material.
In operation, one or more filter cartridges are mounted within a filter system. The filter system includes a filter housing that is usually similar in shape to the filter cartridge, but large enough to contain one or more filter cartridges positioned end to end. For example, it is not uncommon for ten (10) or possibly more filter cartridges to be positioned end to end within a single filter housing. An inlet is provided, typically connected to the peripheral wall of the filter housing, for introducing unfiltered fluid into the filter housing. Likewise, a perforated center pipe is provided for supporting and positioning the plurality of filter cartridges within the filter housing, as well as for draining fluid that has passed through the filter cartridges.
The shape and size of the filter housing center pipe corresponds to the apertures provided through the planar end walls of each filter cartridge. Each filter cartridge thus may be mounted within the housing by inserting the center pipe through the apertures. In this manner, unfiltered fluid is introduced into the filter housing by the inlet and directed inwardly through the filter material for filtration before passing through the perforations of center pipe, such that filtered fluid is drained back to the fluid system for reuse.
Gaskets, typically made of felt or other deformable material, are placed on the housing center pipe between the planar ends of adjacent filter cartridges, as well as at each extreme end of the plurality of filter cartridges. The purpose of the felt gaskets is two-fold. First, the gaskets are provided to seal the exposed perforations along the housing center pipe between adjacent filter cartridges. Second, the gaskets are intended to seal the annular gap created proximate the planar ends of each filter cartridge between the apertures and the center pipe of the fluid housing.
Unfortunately, the effectiveness of the gaskets in sealing against leakage is typically limited, particularly once filtration has been initiated. This is because contaminants that collect on the filter material tend to restrict flow through the filter cartridges. If sufficient back pressure develops within the filter housing due to this flow restriction, unfiltered fluid finds a less restrictive flow path between the planar end of a filter cartridge and the adjacent gasket rather than through the filter cartridge itself. Additional factors that attribute to leakage include undetected defects in either the gaskets or the planar ends of the filter cartridges, which prevent full surface contact therebetween, and deflection of the housing center pipe due to the weight of the filter cartridges, thus causing nonuniform pressure on the gaskets by the planar ends of the filter cartridges.
To some extent, it has been determined that the effectiveness of the gaskets may be improved by increasing the compression on the gaskets against the planar ends of the filter cartridges. This may be performed by tightening a threaded nut on the end of the housing center pipe so as to press the filter cartridges and gaskets against each other. It is believed, however, that only little benefit is achieved by this tightening process since the threat of stripping the threaded end of the center pipe or deforming the planar end walls limits the extent of compression available.
In view of the above, there remains a need for a cost effective method and apparatus for preventing leakage of unfiltered fluid through filter systems using filter cartridges.